The method of pore volume determination is essential to the characterization of our invention. Nitrogen desorption and mercury penetration techniques indicate virtually no pores above 100 A in diameter. However, nitrogen absorption techniques indicate that up to 30% of the total pore volume exists in this region. This disagreement is a well-known phenomena and thought to occur as a result of the pore configuration. Pores which are cylindrical in shape will give similar nitrogen absorption and nitrogen desorption isotherms. Irregularly shaped pores or "ink bottle" shaped pores will have significantly different pore volume distributions depending on the method of determination. For "ink bottle" shaped pores or pores having narrow entrances, the nitrogen desorption and mercury intrusion pore volume distributions are thought to be representative of the size of the pore opening or pore orifice. However, nitrogen adsorption is not influenced by the pore opening but rather reflects the average diameter profile of the entire pore. This difference is important in characterizing catalysts since the size of the pore opening or orifice will act as a screen to the size of molecule which can diffuse into the catalyst. The alumina made by the use of our invention gives pore volume distributions which are typical of those thought to be caused by restricted or narrow necked openings to pores.
Thus, the novel alumina described in this invention provided an improvement in the art in that it allows molecules of a selective size to pass through an orifice into an enlarged pore cavitiy where maximum surface area is available for reaction.